Preparation method of octamethylcyclotetrasiloxane adsorbent

Abstract

The invention provides a preparation method of an octamethylcyclotetrasiloxane adsorbent. The adsorbent is a DUT-4-phosphoric acid modified adsorbent prepared by adopting aluminum ions and 2, 6-naphthalene dicarboxylate to form a coordinate bond to form DUT-4 and then loading a phosphoric acid ligand on the DUT-4 in a chemical bonding manner. The phosphoric acid modified adsorbent prepared by the method has the characteristics of high adsorption efficiency, large adsorption capacity and easiness in regeneration, the thermal contact time in the production process of the low-viscosity methyl silicone oil is shortened, and the equipment cost and the energy consumption are reduced.

Description

Technical Field

[0001] The invention belongs to the field of organic silicone oil production, and specifically relates to a method for preparing an octamethylcyclotetrasiloxane adsorbent. Background Art

[0002] Low-viscosity methyl silicone oil has the advantages of high dispersibility, low surface tension, low reactivity, low vapor pressure, good thermal stability and leveling, and has good compatibility with most cosmetic ingredients. Therefore, it is widely used in the daily chemical industry, among which 1.0-2.5 cst decamethyltetrasiloxane (MD2M) has unique application prospects. However, compared with imports, domestically produced low-viscosity methyl silicone oil has high impurity content (octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5) and dodecamethylcyclohexasiloxane (D6) are difficult to remove deeply) and dark color.

[0003] At the European Chemicals Agency PBT Working Group meeting held in March 2008, D4 and D5 were included in the list of chemicals that need further evaluation for the first time. Since then, Canada, Norway, the United States, Australia, Japan and other countries have carried out risk assessment and environmental monitoring of volatile cyclosiloxanes (cVMS). Some studies have shown that octamethylcyclotetrasiloxane has long-term harmful effects on the aquatic environment and has the risk of weakening reproductive capacity. Octamethylcyclotetrasiloxane mainly enters the environment through volatilization, wastewater and other means, accumulates in organisms, and produces biological hazards. Octamethylcyclotetrasiloxane is considered to have PBT (persistent, bioaccumulative, toxic) substances and vPvB (very persistent, very bioaccumulative) substances, while decamethylcyclopentasiloxane and dodecamethylcyclohexasiloxane are identified as vPvB substances. In January 2018, octamethylcyclotetrasiloxane and decamethylcyclopentasiloxane were listed as restricted substances in Annex XVII of REACH Regulation. On June 27, 2018, ECHA announced the 19th batch of substances of very high concern (SVHC), and octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane and dodecamethylcyclohexasiloxane were listed as substances of very high concern in REACH Regulation.

[0004] To remove octamethylcyclotetrasiloxane from low-viscosity decamethyltetrasiloxane silicone oil, the following methods can be used: distillation method, because octamethylcyclotetrasiloxane and other substances have different boiling points, they can be separated by distillation. However, this method consumes a lot of energy and has high equipment costs. Adsorption method, mainly through some adsorbents with rich pore structures or large specific surface areas to achieve the removal of octamethylcyclotetrasiloxane, the adsorption process includes chemical adsorption, physical adsorption, exchange adsorption and other adsorption types, the adsorption effect is affected and restricted by factors such as the surface chemical properties and structural characteristics of the adsorbent, the molecular size of the adsorbate and its physicochemical properties, and the adsorption environment.

[0005] The adsorption method has the advantages of high adsorption efficiency, simple process equipment, small footprint, cheap and easy-to-obtain consumables, etc. However, most adsorbents have selective adsorption properties. The adsorption performance can be improved by modifying the adsorbent, thereby improving the removal capacity of difficult-to-degrade organic matter. However, general adsorbents are expensive and have low regeneration rates. Therefore, seeking an efficient adsorbent with large adsorption capacity and high regeneration rate is the focus of adsorption research. At present, there is a lack of efficient adsorption materials for the adsorption and removal of octamethylcyclotetrasiloxane. Summary of the invention

[0006] The purpose of the present invention is to provide a method for preparing an octamethylcyclotetrasiloxane adsorbent, and the preparation process of the adsorbent is as follows: 1. Mix 2,6-naphthalene dicarboxylic acid and aluminum nitrate nonahydrate in a certain proportion and dissolve them in N,N-dimethylformamide.

[0007] 2. Add the above mixed solution into a reactor and heat it to 100°C~160°C, react at this temperature for 18~30 hours, and naturally cool to room temperature after the reaction to obtain the initial product.

[0008] 3. Wash the initial product 3 to 5 times with N,N-dimethylformamide, and then centrifuge and filter at 10,000-15000 rpm for 2 to 4 min to remove impurities such as unreacted products.

[0009] 4. Dry the centrifuged product at 100-140°C for 4-6 hours to ensure that the product is completely dry, thereby obtaining the adsorbent DUT-4.

[0010] 5. Mix the DUT-4 obtained in the previous step with the phosphorylation reagent in a certain proportion and stir for 8 to 12 hours and then age for 1 to 2 hours.

[0011] 6. The material obtained after aging is sintered at 300-450° C. to obtain the DUT-4-phosphoric acid modified adsorbent.

[0012] The mass ratio of 2,6-naphthalene dicarboxylic acid to aluminum nitrate nonahydrate is 1-5.5-6.5.

[0013] Among them, the solid-liquid ratio of 2,6-naphthalene dicarboxylic acid to N,N-dimethylformamide g:mL is 1 / 200~1 / 100.

[0014] Wherein, the phosphorylation agent is selected from aluminum dihydrogen phosphate, dialkyl phosphate, ammonium dihydrogen phosphate, ammonium hydrogen phosphate, sodium hydrogen phosphate, or sodium hypophosphite.

[0015] The solid-to-liquid ratio (g:mL) of DUT-4 to phosphorylation reagent in the preparation process should be 1 / 100 ~1 / 40.

[0016] The DUT-4 can also be replaced by MOF-806 or PCN-223. The DUT-4, MOF-806 and PCN-223 used are all commercially available products, or can be prepared by known methods.

[0017] Another technical solution of the present invention is to provide a phosphoric acid modified adsorbent prepared by the above method. The phosphoric acid modified DUT-4 adsorbent has a bulk density of 0.35-0.9 g / mL and a specific surface area of ​​500-1050 m 2 / g, pore volume is 0.4-1.0mL / g; Another technical solution of the present invention is to provide a phosphoric acid modified adsorbent prepared by the above method. The phosphoric acid modified MOF-806 adsorbent has a bulk density of 0.45-0.88 g / mL and a specific surface area of ​​400-900 m 2 / g, pore volume is 0.5-1.0mL / g; Another technical solution of the present invention is to provide a phosphoric acid modified adsorbent prepared by the above method. The phosphoric acid modified PCN-223 adsorbent has a bulk density of 0.40-0.95 g / mL and a specific surface area of ​​450-900 m 2 / g, pore volume is 0.5-0.9mL / g; Another technical solution of the present invention is to provide the use of the phosphoric acid modified adsorbent prepared by the above method in the selective adsorption of octamethylcyclotetrasiloxane.

[0018] Features and effects of the present invention: The prepared phosphoric acid modified adsorbent has the advantages of high adsorption efficiency and large adsorption capacity for cyclic siloxane D4 in low-viscosity silicone oil. When separating products by a simple distillation method, the heat contact time is long, and it is difficult to ensure the purity and color of the product. The present invention removes D4 by using an adsorption column filled with a high-efficiency adsorbent, which reduces the heat contact time, equipment cost and energy consumption.

[0019] Through phosphoric acid modification, the chemical properties of the adsorbent surface have been finely regulated, more acidic groups have been introduced, and the charge distribution has been changed. These changes directly enhance the interaction with the D4 molecules, thereby significantly improving the adsorption effect. Secondly, the modification process is often accompanied by the expansion of the specific surface area of ​​the adsorbent and the optimization of the pore structure, which not only provides more adsorption sites for the D4 molecules, but also promotes the diffusion and adsorption of the D4 molecules inside the adsorbent, further improving the adsorption capacity and efficiency.

[0020] In terms of durability, phosphoric acid-modified adsorbents also perform well. The modification process not only enhances the stability of the adsorbent's internal structure, but also improves its ability to resist pollution and wear. This enables the adsorbent to maintain high adsorption efficiency and stability during long-term use, extending its service life and reducing replacement costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0022] Figure 1 The invention discloses a method for preparing an octamethyl-tetrasiloxane adsorbent. DETAILED DESCRIPTION

[0023] The technical scheme of the present invention will be further described in detail below in conjunction with specific embodiments. It should be understood that the following embodiments are only exemplary illustrations and explanations of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are included in the scope of protection that the present invention is intended to protect.

[0024] Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available or can be prepared by known methods.

[0025] Example 1 A method for preparing dialkyl phosphate modified MOF-806 comprises the following steps: 0.38 g of MOF-806 was placed at 120° C. and dried for 4 h to remove moisture.

[0026] The dried MOF-806 was mixed with dialkyl phosphate at a solid-to-liquid ratio (g:mL) of 1:50 and stirred for 12 h and then aged for 2 h. The material obtained after aging was sintered at 350° C. to obtain 0.45 g of the dialkyl phosphate modified MOF-806 adsorbent.

[0027] Example 2 A method for preparing sodium hypophosphite-modified PCN-223 comprises the following steps: 0.32 g of PCN-223 was placed at 120° C. and dried for 4 h to remove moisture.

[0028] The dried PCN-223 was mixed with sodium hypophosphite at a solid-to-liquid ratio (g:mL) of 1:60 and stirred for 12 h and then aged for 2 h. The material obtained after aging was sintered at 450° C. to obtain 0.48 g of the sodium hypophosphite-modified PCN-223 adsorbent.

[0029] Example 3 A method for preparing a diammonium phosphate-modified DUT-4-phosphoric acid modified adsorbent comprises the following steps: 0.26 g of 2,6-naphthalenedicarboxylic acid was mixed with 30 mL of N,N-dimethylformamide and aluminum nitrate nonahydrate.

[0030] The mixed solution was transferred to a 250 mL reactor, and the reactor was placed in an oven and heated at 120° C. for 24 h. After the heating was completed, the reactor was taken out and allowed to cool naturally to room temperature to obtain the initial product.

[0031] The obtained initial product was washed three times with 20 mL of N,N-dimethylformamide, and centrifuged at 10,000 rpm for 2 min after each washing to remove unreacted impurities.

[0032] The product after centrifugation was transferred to an oven and dried at 120°C for 4 h to obtain 0.39 g of DUT-4 adsorbent product.

[0033] The DUT-4 obtained in the previous step was mixed with ammonium dihydrogen phosphate at a solid-liquid ratio (g:mL) of 1:60 and stirred for 10 hours and then aged for 1 hour. The material obtained after aging was sintered at 350° C. to obtain 0.43 g of the diammonium phosphate-modified DUT-4-phosphoric acid-modified adsorbent.

[0034] Example 4 A method for preparing a DUT-4-phosphoric acid modified adsorbent modified with ammonium hydrogen phosphate, comprising the following steps: 0.35 g of 2,6-naphthalenedicarboxylic acid was mixed with 40 mL of N,N-dimethylformamide and aluminum nitrate nonahydrate.

[0035] The mixed solution was transferred to a 250 mL reactor, and the reactor was placed in an oven and heated at 140° C. for 18 h. After the heating was completed, the reactor was taken out and allowed to cool naturally to room temperature to obtain a primary product.

[0036] The obtained initial product was washed three times with 20 mL of N,N-dimethylformamide, and centrifuged at 10,000 rpm for 2 min after each washing to remove unreacted impurities.

[0037] The product after centrifugation was transferred to an oven and dried at 120°C for 5 h to obtain 0.59 g of adsorbent DUT-4 powder.

[0038] The DUT-4 obtained in the previous step was mixed with 8-ammonium hydrogen phosphate at a solid-to-liquid ratio (g:mL) of 1:80 and stirred for 10 h and then aged for 1 h.

[0039] The material obtained after aging was sintered at 350° C. to obtain the 0.64 g DUT-4-phosphoric acid modified adsorbent of ammonium hydrogen phosphate.

[0040] Example 5 A solution of MD2M containing 1000ppm D4 was prepared, and the modified adsorbent prepared in Examples 1-4 was used for adsorption removal test. An adsorption column with a diameter of 20mm and a length of 300mm was selected, and the modified adsorbent was filled in the adsorption column with a filling rate of 80%. Under the conditions of adsorption pressure of 0.2MPaG and adsorption temperature of 30°C, a solution of MD2M containing 1000ppm D4 was passed through the adsorbent at a rate of 0.1L / min. The results are shown in the following figure:

[0042] In combination with specific examples 1-4, the phosphoric acid modified adsorbents all showed efficient adsorption capacity for D4. At room temperature, the phosphoric acid modified adsorbent can significantly reduce the D4 content in MD2M to an extremely low level. However, the heat contact time when separating the products by a simple distillation method is long, and it is difficult to ensure the quality of the products. The present invention removes D4 by using an adsorption column filled with a high-efficiency adsorbent, which reduces the heat contact time while reducing equipment costs and energy consumption. The phosphoric acid modified adsorbent prepared by the present invention has high application value in removing impurities such as D4 in MD2M due to its advantages such as efficient adsorption performance, good thermal stability, easy preparation, good operational adaptability, environmental protection and safety.

[0043] Finally, it should be noted that the above-described embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the present invention. Although the present invention has been described in detail with reference to the above-described embodiments, those skilled in the art should understand that the technical solutions described in the above-described embodiments may still be modified, or some or all of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing an octamethylcyclotetrasiloxane adsorbent, characterized in that: The preparation process comprises the following steps: (1) Mix 2,6-naphthalene dicarboxylic acid and aluminum nitrate nonahydrate in a certain proportion and dissolve them in N,N-dimethylformamide; (2) adding the above mixed solution into a reaction kettle and heating it to 100°C to 160°C, reacting at this temperature for 18 to 30 hours, and naturally cooling to room temperature after the reaction to obtain a primary product; (3) Wash the initial product 3 to 5 times with N,N-dimethylformamide, and then centrifuge and filter at 10,000-15,000 rpm for 2 to 4 minutes to remove impurities such as unreacted products; (4) Drying the centrifuged product at 100-140° C. for 4-6 hours to ensure that the product is completely dry, thereby obtaining the DUT-4 adsorbent; (5) Mix the DUT-4 obtained in the previous step with the phosphorylation reagent in a certain solid-liquid ratio and stir for 8 to 12 hours and then age for 1 to 2 hours; (6) The material obtained after aging is sintered at 300°C-450°C to obtain a phosphoric acid modified adsorbent.

2. The preparation method according to claim 1, characterized in that: The mass ratio of 2,6-naphthalenedicarboxylic acid to aluminum nitrate nonahydrate should be 1~5.5-6.

5.

3. The preparation method according to claim 1, characterized in that: The solid-liquid ratio (g:mL) of 2,6-naphthalene dicarboxylic acid and N,N-dimethylformamide should be 1 / 200~1 / 100.

4. The preparation method according to claim 1, characterized in that: The phosphating agent is selected from aluminum dihydrogen phosphate, dialkyl phosphate, ammonium dihydrogen phosphate, ammonium hydrogen phosphate, sodium hydrogen phosphate, or sodium hypophosphite.

5. The preparation method according to claim 1, characterized in that: The solid-liquid ratio (g:mL) of DUT-4 and phosphorylation reagent should be 1 / 100 ~1 / 40.

6. The preparation method according to any one of claims 1 to 5, characterized in that: The DUT-4 can also be replaced by MOF-806 or PCN-223.

7. Use of the phosphoric acid-modified adsorbent prepared by the preparation method according to any one of claims 1 to 6 for selectively adsorbing octamethylcyclotetrasiloxane.

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